The United States has the world's largest coal reserves estimated at 6 trillion tons, and coal is the nation's most abundant fossil fuel resource. Unfortunately, 90 percent of the coal is un-mineable due to seam thickness, depth, and structural integrity. One way that the nation's substantial un-mineable coal resources can produce energy is through the extraction of coal bed natural gas (CBNG) which is primarily methane (coal-bed methane (CBM)) absorbed on coal surfaces and held in place by the hydrostatic pressure exerted by groundwater. Water is pumped out of the seam to the surface through wells that are screened along the coal seam in order to release the pressure, which eventually allows the methane to desorb from the coal surface for extraction. Unlike coal, CBM is clean-burning and its recovery requires minimal surface disruption. For the sub-bituminous coal that is produced in the Powder River Basin (PRB) of Wyoming and Montana, there are 200,000 lb of CO2, 2,800 lb of particulates, and 0.02 lb of mercury produced per billion BTU of energy output. By comparison, natural gas produces 100,000 lb of CO2, 7 lb of particulates, and 0 lb of mercury. Constituents causing acid rain such as sulfur dioxide and nitrogen oxide are also significantly reduced. Natural gas costs, on average, are more than one-third lower than conventional gas at the pump, and natural gas has been 25-42 percent less expensive than diesel over the last 14 years. Natural gas is also used as the hydrogen source for many fuel cells, and burning natural gas heats the majority of homes in the U.S.
The estimated total CBNG within the PRB, located in Wyoming and Montana, is 39 trillion cubic feet (TCF), of which about 90% is located in the Wyoming portion of the basin. In the early 1990's, several small CBNG companies began producing natural gas and produced water from coal seams located within the PBR. To date, there have been nearly 30,000 wells drilled in the PRB. CBNG has constituted a significant proportion of the total U.S. production of natural gas over the past two decades, with annual production increasing to 1.8 TCF or approximately 9% of total production.
The principal constituent in CBNG is methane (sometimes referred to as coal bed methane ((CBM)), with trace levels of propane, butane, N2, and O2. Extraction requires a significant capital investment in gas-collection and water-management infrastructure, including extraction wells, separators, compressors, pipelines, outfalls, and evaporation ponds, but the average operational life of a CBNG well is less than 8 years. Consequently, much of the infrastructure used for CBNG production is decommissioned or abandoned as coal beds become depleted, which represents a significant loss with respect to capital expenditures, existing infrastructure, and inefficient use of resources.